Detection and measurement of penetrative radiation



y 5, 1956 c. G. LUDEMAN 2,745,963

DETECTION AND MEASUREMENT OF PENETRATIVE RADIATION Original Filed March12, 1949 I N V EN TOR. C4 /FFOPD G UDE/l l/l/V BY M/ ATTORNEY? UnitedStates Patent G DETECTIGN AND PAEASUREMENT OF PENETRATIVE RADIATIONClifford G. Ludeman, Scarsdale, N. Y., assignor to Texaco DevelopmentCorporation, New York, N. Y., a corporation of Delaware Originalapplication March 12, 1949, Serial No. 81,098,

now Patent No. 2,559,219, dated July 3, 1951. Divided and thisapplication lyiay 1, 1951, Serial No. 223,981

6 Claims. (Cl. 25071) This invention relates to the detection andmeasurement of penetrative radiation such as gamma rays and moreparticularly to phosphor elements for such purposes.

Certain substances such as naphthalene, zinc sulfide, and zinc silicatehave been found to possess the property of converting penetrativeradiation such as gamma rays to radiation in other ranges of thespectrum such as the ultraviolet range and the visible light range. Suchsubstances are called phosphors and their utilization in the detectionof such penetrative radiation has been practiced to some extent. In thesimpler arrangements, the phosphor is subjected to penetrativeradiation, the converted radiation radiated from the phosphor beingdetected and measured in an electron multiplier of the tube type.

The use of such phosphors or fiuorphors has been limited in manyparticulars. For instance, it is necessary that the dimension of eachphosphor be kept below a certain critical dimension. This dimension isusually considered to be the maximum dimension at which the radiationgenerated or developed in the phosphor can escape therefrom and abovewhich the phosphor will absorb such radiation so that the amount ofradiation discharged from the phosphor corresponds to only thatgenerated within the critical dimension as measured from the radiatingsurface. A further limitation is found in the fact that some phosphorssuch as naphthalene, anthracene and scheelite, are not in convenientphysical forms for handling or for shaping as desired.

In overcoming the aforesaid disadvantages and in providing an improvedphosphor or fluorescent element, it is an object of the invention toprovide a phosphor element wherein the dimension as respects theself-absorption thereof for the radiation generated therein is notlimiting and the element can be employed in almost any mass desired.

Another object of the invention is the provision of a novel phosphorelement which can be shaped as desired and accommodated to anyparticular use in a manner to function with maximum elficiency.

Other objects and advantages of the invention will appear from thefollowing description and claims taken in connection with the attacheddrawings wherein:

Fig. 1 represents a phosphor element wherein the phosphor is combinedwith a solid conductor in a solid phase.

Fig. 2 is a perspective of a phosphor element similar to that of Fig. 1wherein the conductor component is in a liquid phase.

Fig. 3 represents a phosphor element similar to that of Fig. 1 but ofdifferent shape.

In brief, the present invention is directed to a phosphor element,capable of converting one type of radiation to another, the elementincluding a phosphor per se distributed as a solid or liquid and as adispersion or a solute, or both in a matrix of a material capable ofbeing shaped as desired and capable of conducting the radiationdeveloped in the phosphor, the phosphor element having at least onesection such as a face for exposure to and interception of thepenetrative radiation to be detected and measured, and at least onesecond section such as a face for exposure to a detecting and measuringdevice capable:

tive radiation to more easily detectable and measurable radiation inother ranges of the spectrum is shown dispersed as a solid in a casting11 of a suitable material for conducting the radiation emitted by thedispersed phosphor masses, the original relatively small effectivedimensions of the original phosphor material for the interception andconversion of penetrative radiation being enlarged to the large volumeor dimensions of the matrix or resultant phosphor element. Such anelement can be formed by dispersing the phosphor masses in a suitableconductor While in a liquid phase, the resultant mixture beingthereafter cast and caused to harden in Well-known manner. While thephosphor masses are shown in the drawing as substantially uniformlydispersed, it is to be understood that they may be disposed otherwise inthe conductor material. For instance, the phosphor masses may beconcentrated along the faces of the matrix or at the center thereof. Anyarrangement or design found most suitable for a particular use of thephosphor element can be used, the phosphor element being considered tobe that portion of the matrix in which the phosphor is distributed.

Suitable phosphors are of both the inorganic and organic types. Typicalinorganic phosphors are natural or synthetic calcium tungstate, zincsulfide and Zinc silicate, or mixtures thereof. Typical organicphosphors include benzoic acid and polynuclear aromatics such asnaphthalene, anthracene or diphenyl and mixtures of the foregoing.Phosphors of the above types and their properties are known. Theypossess the unique characteristic of being able to convert penetrativeradiation such as gamma rays to radiation in other ranges of thespectrum such as the ultraviolet and visible light ranges which is moreeasily detectable and measurable directly by relatively simple means.

Radiation conductors which have been found excellent for support of thephosphor include polystyrene and poly merized methyl methacrylate, thelatter being commercially available under the trade names of Lucite,Plexiglas and Crystallite. A polyester now being commercially sold asCastolite has also been used.

The phosphor and the conductor may be combined in; a liquid or solidphase or in a gel-like or semisolid phase. In Fig. 1 wherein particlesof the phosphor are'visible, the phosphor has been added to theconductor material in excess of any solubility it may have in theconductor, the two being subsequently cast together to form a solidelement.

In Fig. 2, a container 13 having a cover 1a, both preferably ofconducting material, is shown with the same or a ditferent conductor 15in the liquid phase contained therein, the phosphor particles 16 beingsuspended there in. While there may be some tendency for the phosphorparticles to settle, this settling may be overcome by shaking thecontainer at intervals. Any tendency to settle can be reduced by using aconductor of high viscosity and reducing the phosphor to fine particlesize.

While the phosphor has been shown in Figs. 1 and 2 in the form of finelydivided masses, it is to be understood that a single mass of thephosphor or a multiplicity of masses of larger size can be used. Thesizes of the individual masses will depend upon the aforesaid criticaldimension and the desirability of avoiding any interference with theescape of radiation from the phosphor elements. Stated otherwise, it isdesirable not to have a density of phosphor particles such that one ormore particles may interfere with the discharge of radiation generatedin another particle. Obviously the critical dimension will vary witheach specific phosphor and can readily be determined.

Preferably the phosphor is divided into relatively fine particles whichadmits of better and more homogeneous dispersion throughout theconductor in either the liquid or solid phase. It the phosphor becompletely or partially soluble in the conductor, the desiredhomogeneity is even more complete.

A marked advantage of such a phosphor element is the ability to form itin almost any dimension Without regard to the critical dimension of the,phosphor, thereby enabling the element to be used more efiiciently.

A further advantage of the phosphor element of this invention is evidentfrom fig. 3 wherein an element has been cast, machined or otherwiseformed in the shape of a truncated cone having a section such as a face17 open or exposed to a penetrative radiation to be determined 7 and aconical side wall 13 which terminates in a small section such as face19, preferably of a size and shape approximating the detecting andmeasuring element such as the cathode of an electron multiplier of thetube type and arranged to be disposed there adjacent. A typical tubetype is the one designated 931A (931A, 1P21, or IP28) now beingmanufactured and sold by Radio Corporation of America.

The side walls of the cone may be coated with a material capable ofreflecting the generated radiation back into the conducting element sothat itis eventually discharged at face 19, silver, aluminum or cadmiumbeing effective for such purposes. If the conductor has a suflicientlyhigh refractive index, such a coating may be omitted to avoid adsorptionof the radiation by the coating.

The application is a division of application Serial No. 81,098 filedMarch 12, 1949, now Patent No. 2,559,219.

Obviously many modifications and variations of the invention ashereinabove set forth may be made without departing from the spirit andscope thereof and only such limitations should be imposed as areindicated in the appended claims.

I claim:

1. A phosphor element for use in the detection and measurement ofpenetrative radiation such as gamma rays comprising calcium tungstate inrelatively small amount having of itself relatively small effectivedimensions for the interception and conversion of penetrative radiationto more easily detectable and measurable radiation in other ranges ofthe spectrum, and a matrix of relatively large volume capable ofconducting said last-named radiation, said calcium tungstate beingsubstantially homogeneously distributed throughout said matrix wherebythe originally relatively small effective dimensions of said cal- 4.-cium tungstate for the interception and conversion of penetrativeradiation are enlarged to the volume of said matrix, the element formedby said calcium tungstate and said matrix being formed with at least onesection for exposure to and interception of penetrative radiation and atleast one second section for exposure to a detecting and measuringdevice capable of detecting and measuring the converted radiation, saidfirst and second sections being spaced from one another to insureexposure of the penetrative radiation to a substantial portion of thevolume of said element.

2. The phosphor element of claim 1 wherein said element excepting saidsecond section is surrounded by a reflector for said convertedradiation.

3. The phosphor element of claim 1 wherein said matrix is formed ofpolystyrene.

4. The phosphor element of claim 1 wherein said matrix is formed ofpolymerized methyl methacrylate.

5. The phosphor element of claim 1 wherein said matrix is in the liquidphase.

6. A phosphor element for use in the detection and measurement or"penetrative radiation such as gamma rays comprising calcium tungstate inrelatively small amount having of itself relatively small eifectivedimensions for the interception and conversion of penetrative radiationto more easily detectable and measurable radiation in other ranges ofthe spectrum, and a matrix of relatively large size capable ofconducting said la" -named radiation, said calcium tungstate beingsubstantially homogeneously distributed throughout said matrix wherebythe original relatively small efiective dimensions of the calciumtungstate for the interception and conversion of penetrative radiationare extended and enlarged to the dimensions of said matrix, the elementformed by the calcium tungstate and the matrix being formed with arelatively large section for exposure to and interception of penetrativeradiation and a relatively small section for exposure to a detecting andmeasuring device capable of detecting and measuring the convertedradiation, said element being shaped between said sections toconcentrate said converted radiation for discharge from said secondsection to said detecting and measuring device.

References Cited in the file of this patent UNITED STATES PATENTS Arenset al. Dec. 17, 1940 Rosenblum Oct. 4, 1943 OTHER REFERENCES

1. A PHOSPHOR ELEMENT FOR USE IN THE DETECTION AND MEASUREMENT OFPENETRATIVE RADIATION SUCH AS GAMMA RAYS COMPRISING CALCIUM TUNGSTATE INRELATIVELY SMALL AMOUNT HAVING OF ITSELF RELATIVELY SMALL EFFECTIVEDIMENSIONS FOR THE INTERCEPTION AND CONVERSION OF PENETRATIVE RADIATIONTO MORE EASILY DETECTABLE AND MEASURABLE RADIATION IN OTHER RANGES OFTHE SPECTRUM, AND A MATRIX OF RELATIVELY LARGE VOLUME CAPABLE OFCONDUCTING SAID LAST-NAMED RADIATION, SAID CALCIUM TUNGSTATE BEINGSUBSTANTIALLY HOMOGENEOUSLY DISTRIBUTED THROUGHOUT SAID MATRIX WHEREBYTHE ORIGINALLY RELATIVELY SMALL EFFECTIVE DIMENSIONS OF SAID CALCIUMTUNGSTATE FOR THE INTERCEPTION AND CONVERSION OF PENETRATIVE RADIATIONARE ENLARGED TO THE VOLUME OF SAID MATRIX, THE ELEMENT FORMED BY SAIDCALCIUM TUNGSTATE AND SAID MATRIX BEING FORMED WITH AT LEAST ONE SECTIONFOR EXPOSURE TO AND INTERCEPTION OF PENETRATIVE RADIATION AND AT LEASTONE SECOND SECTION FOR EXPOSURE TO A DETECTING AND MEASURING DEVICECAPABLE OF DETECTING AND MEASURING THE CONVERTED RADIATION, SAID FIRSTAND SECOND SECTIONS BEING SPACED FROM ONE ANOTHER TO INSURE EXPOSURE OFTHE PENETRATIVE RADIATION TO A SUBSTANTIAL PORTION OF THE VOLUME OF SAIDELEMENT.